南美Oriente盆地北部海绿石砂岩油藏特征及成藏规律

南美厄瓜多尔Oriente盆地斜坡带发育的白垩系Napo组高伽马特征的UT海绿石砂岩段是成熟探区新发现的隐蔽含油层段。本文分析了海绿石砂岩储层的矿物组成、孔隙结构、成岩作用、物性特点,并结合烃源岩评价与石油空间分布探讨海绿石砂岩油藏的成藏特征。海绿石粘土矿物以颗粒形式存在,与石英共同构成海绿石砂岩的颗粒组分,海绿石砂岩的孔隙结构具有双峰特征,束缚水含量高,属于中-低孔、中-低渗储层类型,孔隙类型主要是剩余粒间孔。海绿石砂岩储层中石英次生加大属Ⅱ级,长石碎屑颗粒发生溶蚀作用,含铁碳酸盐类胶结物发育,结合泥岩低的I/S混层比和高的最高峰温值T_max,指示海绿石砂岩层段属于中成岩阶段A期的产物。与海绿石砂岩油藏紧邻的大面积分布的Ⅱ₁腐泥型成熟烃源岩就是缓翼斜坡带的生烃中心,大面积连续发育的海绿石砂岩与之构成优越的源储组合,有利于上生下储式成藏。海绿石砂岩油藏表现为近源性、成藏晚期性等特点,规模发育的海绿石砂岩储层得以成藏的主要运聚机制是体积流和扩散流运聚机制。这对盆地其它油区同类油藏的发现具有重要的借鉴意义。

Hydrocarbon accumulation and enrichment of glauconitic sandstones in North Oriente Basin,South America

Glauconitic sandstone with high GR value of the Cretaceous Napo Formation, developed in the slope of the Oriente Basin, is a new discovered subtle oil-bearing target. This paper is focused on glauconitic sandstone reservoir to reveal its components, porosity structure, diagenesis, petrophysics. Integrated with source rock evaluation and oil distribution, hydrocarbon accumulation and enrichment of glauconitic sandstone are analyzed. Glauconitic sandstone is composed of quartz and glauconitic minerals, characterized by grain-supported framework. Glauconitic sandstone reservoir is low-mid porosity and permeability, characterized by residual intergranular pores. NMR data shows bimodal pore structure and high bound water content. Glauconitic sandstone is the product of phase A of middle diagenetic stage, based on evidences of quartz overgrowth cementation Ⅱ, feldspar dissolution, iron carbonate cements, low-value of smectite in I/S ratio, and high T_max. Large-area type Ⅱ₁ matured shale closes to glauconitic sandstone is probably the oil kitchen in the gentle slope of Oriente Basin. Widespread glauconitic sandstone reservoir and adjacent shale form an excellent source-reservoir-cap assemblage. Glauconitic sandstone play is characterized by closing to source rock, late migration and single accumulation type. It provide a paradigm for petroleum exploration of glauconitic reservoir in similar basin.